Volcanogenic sedimentation in the Iceland Basin: influence of subaerial and subglacial eruptions

Abstract

Cores recovered from the Iceland Basin show evidence of transport and deposition of volcaniclastic sediment from the Eastern Volcanic Zone of Iceland during the Holocene and last glacial period. Three types of deposits have been identified: tephra fall, sediment gravity flows, and bottom-current-controlled deposits. Tephra fall layers contain basaltic glass of composition that suggests Katla volcano as the major source. A chronology of the volcano activity is reconstructed, back to isotopic stage 5d (120,000 yr). Glass chemistry of tephra in sediment gravity flows deposited south of Myrdalsjökull Canyon indicates a source in the Grı́msvötn–Lakagı́gar volcanic system. These volcaniclastic gravity flows were most likely derived from jökulhlaups or large glacial floods, at a time of a more extensive ice cover over the volcanic zone. Deposition of the sediment gravity flows has created a deep-sea fan south of the canyon. Basalt glass composition, age, and depositional environment suggest that one early Holocene turbidite sequence was derived from a large jökulhlaup of the Grı́msvötn area. The volcanogenic sediment gravity flows were influenced by a strong contour current, moving across the Katla sediment ridges. The contour current has winnowed the silt fraction and transported it downstream as suspended load. The recovery of numerous silty volcaniclastic layers, enriched in detrital crystals, indicates that they contributed to the sedimentation of contourite drifts.